World Audio Kel 80 User manual

KEL80
INTEGRATED
INSTRUCTION
MANUAL
TEXT ONLY
KEL80 instructions 27/3/00 10:44 am Page 1

SAFETY WARNING
Lethal voltages exist in this amplifier. Even though this is one of our simplest kits, in terms of
construction, please do not attempt to build it unless you have some understanding of valve circuitry
and can follow safety precautions.
We do provide a back-up service, a help-line is manned from 9.00am to 5.00pm Monday to
Friday, should you run into any problems. Additionally, if the worst comes to the worst and you
encounter problems, ,we will get you amplifier up and running, for a nominal charge .
For safety, never hold earthed metal work when testing. Make sure your body is isolated by
rubber soled shoes. To aid construction use a voltmeter, one capable of reading up to 1000 volts
would be adequate. YOU MUST WEAR THE RUBBER SAFETY GLOVES PROVIDED when test-
ing, since the greatest danger comes from a slip at this time. Always remove the mains plug when
you are soldering after switch on. The larger power supply capacitors will hold a charge after switch
off, so continue to wear your gloves at all times when working internally.
Additionally be aware that the valves do get very hot and will burn skin on contact, therefore
please position in a safe place, away from children and animals. Due to the compact size of the
amplifier the chassis`s top surface does get hot and the front panel will be warm to the touch.
FUSE
This amplifier consumes 1A from the mains and must be fitted with a 1.6A SLOW-BLOW
fuse. If this blows, then there is a fault and it must be cleared before another fuse is re-inserted. Do
not use a higher rated fuse as you may burn out your transformers and always use the slow-blow
type.
OUTPUT TRANSFORMERS
When it comes to switch on you should always have your output transformers connected up
to a 8 ohm or a 4 ohm load, depending on which taps you have wired up, be it a dummy load (high
power resistor) or a pair of speakers. This is because the load is an integral part of the circuit, unlike
most transistor amplifiers. Switch on without a load will cause unnecessary distress to the output
transformers and failure if left in this state for a long time.
READING
Before you start building read through the instruction at least twice to avoid any mistakes.
All rights to the design are held by World Audio Publishing Ltd. No part of this manual may be
reproduced without Copyright permission from the Company. The kit is for private constructors only.
It is not to be re-sold or in any way used for commercial gain or profit without express written per-
mission from World Audio Publishing Ltd.
World Audio Publishing Ltd.
Imex House
Kilburn Park Rd
LONDON NW6 5LF.
HELP-LINE 0171 625 8032
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INTRODUCTION
KEL 80 monobloc is an inexpensive valve monoblock amplifier capable of providing no less
than 80 watts into an 8 ohm load. This is enough power to satisfy those who feel the usual valve
amp power of around 20 watts insufficient for their needs. The KEL 80 operates in Class AB, run-
ning in Class A at low signal levels to ensure distortion does not colour music at ordinary volumes. It
is possible to bridge two monoblocs by paralleling the inputs and outputs, this delivers an amazing
160 watts into a 4 ohm load.
The KEL 80 uses a ultra quiet encapsulated toroidal mains transformers and a large high
quality E/I output transformer to achieve a broad frequency response that will not waver even at full
power. All valves, rectifiers and the passive components are mounted directly onto the large printed
circuit board, thus improving ease of build compared with its hard-wired counterparts.
The circuit is similar to our popular KEL34 in that it uses the venerable 6AU6, directly cou-
pled to a common cathode phase-splitter, the high power, high transconductance 5687. The output
stage is four EL34 from Tesla (J.J. branded), in parallel push-pull
Simon Pope HFW editor says, “The KEL 80 manages to combine tube refinement and brute
power in a two-box package. Opening with some classical tunes, the KEL80s brought out the depth
of the orchestration as only valve amplification can, crisp, solid bass and lightning-fast transients
coupled with an addictive smoothness to precussion and violins. It takes an amp with genuine con-
trol and grunt to bring out the full bass potential of `Mindfields`, and the KEL80s were well up for the
job. They succeeded in reproducing that rare bass `bounce` that is rarely found in valve gear and
almost never in solid state.”
At this price, the amp is second to none and will open up the benefits of valve amplification to
all you high power audio nuts.
MEASURED PERFORMANCE
power................................................................78watts into 8 ohms
frequency response.......................................................24Hz-96kHz
separation.................................................................................60dB
noise......................................................................................-110dB
sensitivity..............................................................................400mV
distortion........................1kHz..1 Watt..0.012%....78 Watts..0.36%
distortion........................10kHz..1 Watt..0.1%........78 Watts..1.2%
SKILL LEVEL
To build this amplifier you must be able to:
a) solder.
b) have some knowledge of valve circuitry.
c) possess a rudimentary understanding of electricity and electronics.
e) have a multimeter and be able to use it.
f) have access to a dummy load or an old pair of speakers.
g) know the precautions necessary to avoid electric shocks from the mains and amplifier
power lines.
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BUILD SEQUENCE
Before you start building it is a good idea to check the parts supplied against your parts list.
Use the “X” column on the parts list to tick off your components. To help you through the build
process you will find to the rear of the manual, diagrams. These will bear correlation to the text and
a footnote in bold type after each section will tell you which diagram to refer to.
FIXING OF THE HARDWARE
1) Mains switch - this snaps easily in place and is located at the front of the chassis.
2) Mains lead - you need to expose 55cm of the 3 core wire for internal wiring, this can be done
using large wire stripers or a Stanley knife. Use the strain relief provided to fix the wire in place.
see fig. 5 page 11
3) BFA speaker socket - they need to be isolated from the chassis. Fit the BFA socket in this
sequence: speaker post attached to black holder - chassis - grey holder - M5 whole washer -
split washer - nut.
4) Phonos socket - these need to isolated from the chassis, hence the use of the M6 fibre washers.
Fit the phono socket in this sequence: phono socket (female) - M6 fibre washer - chassis - M6
fibre washer - solder tag - nut. see fig. 4 page 11
5) Output transformer (O/P T) - Insulation from the chassis is important so pay careful attention to
page 11. It is of no consequence which way around you fit the O/P T.
6) Mains transformer - The flying leads of the mains transformer are orientated to utilise the
pre-drilled holes on the chassis. The fixing bolt is used in this instant for the chassis earth. So
before fitting the mains transformer, scratch off the paint internally around the fixing hole with a
small flat head screw driver. This ensures good electrical contact with the solder tag, this will be
soldered up later.
POPULATING THE PRINTED CIRCUIT BOARD (PCB)
You will see that the PCB has tracks on both sides. It is important that you can identify which side is
which. The side with all the labelling on, the “ident”, consisting of outlines, positions and the names
of components and tabs, is called the “component side”, this is where all the components sit. The
other side we have termed the “valve base side” as all the valve bases sit here. The PCB is of the
double sided variety, which basically means that a pin (hole) that appears on both sides of the PCB
is not electrically joined even though it is only the thickness of the PCB away from each other. The
pin is joined by threading a piece of wire (usually in the form of component lead) through the pin
and soldering both sides. Please note that there is one pin that is not related to a component, but
needs to be threaded in a similar manner with a piece of wire and soldered both sides. This is
denoted ` PTH ` on the PCB. There is an exception to the rule, namely, all the electrolytic,
polypropylene capacitors and bridge rectifiers, these actually cover the pins on the component side,
thus making it impossible to solder here. Additionally, there are heater links and inter-PCB links to
be made, these are basically lengths of wire joining together two pins on the PCB, these are illus-
trated on page 9.
A GUIDE TO POPULATING THE PCB
1) Insert the terminal pins provided into tabs 1 to 19 to ease all PCB to external connections once
the PCB is fitted into the chassis. You will need to push the terminal pins in place either by using
a pair of snipe nose pliers or by heating the pin, once partially inserted, with your soldering iron,
exerting a downward force, do not push too hard or you will snap your iron. Remember to solder
both sides of the pin. see page 8
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2) Start soldering all the resistor first.
3) All the high wattage resistors (above 1 watts) generate heat, thus, it is a good idea to give them
at least 15mm clearance from the PCB to avoid tarnishing of the board. These resistors are the
following: R1, R2, R7, R8, R13, R14, R19 and R27.
4) Solder in all the capacitors, Note well, C1 - C10, C14 are all electrolytics and only need
soldering on the valve base side. Make sure all these electrolytics are correctly orientated as
they will blow. The polarity is marked on the PCB. see fig. 1 page 11
5) Similarly, C11 and C12 only need soldering on the valve base side.
6) Solder in all the bridge rectifiers. Here, you only need solder them on the valve base side.
Orientation is very important. The PCB is marked clearly, but pay close attention
to fig. 2 page 11
7) Solder in the fuse holder, insert the 1.6A slow blow fuse and position fuse cover.
8) Solder in the valve bases so that they are sitting on the valve base side of the PCB. To reduce
any unnecessary stress to the PCB it is a good idea to insert the EL34 valves into their octal
bases a few times before you solder the bases on the PCB. The orientation of the octal valve
base is very important it is marked by a key-hole (large hole, small key) shape on the PCB, this
correlates to the shape of the central hole of the octal base. The B7G and B9A will only fit in one
positon.
9) Wire in the heater links and the PCB inter - links on the valve base side. see page 9
10) Solder in the wire link that connects the anode of V2 to the anode of V4, denoted by a white line
and `link V4A` on the component side.
FIXING OF THE PCB
1) Using the 6 x M3 x 10 pan head screws and the 8 x M3 fibre washer provided, fit the PCB in
place.
WIRING UP THE SIGNAL INPUTS
1) Take 50cm of single screen cable and wire one end to the phono socket on the back panel, the
red signal section to the centre spigot and the screened section to the phono socket solder tag.
2) Wire the other end to the PCB, the red signal section to PCB tab 10 and the screened section to
PCB tab 9. see page 8
WIRING UP THE MAINS
1) With the mains lead now fitted cut the brown wire 25cm from the end and solder the cut-off
piece to the mains switch and the other end of the cut off piece to PCB tab 2. see fig. 3 page
11 and page 8
2) Solder the blue wire from the mains lead direct to the mains switch. see fig. 3 page 11
3) Solder the brown wire of the mains lead to PCB tab 1. see page 8
4) For 240V operation solder together the violet and grey(thin) leads and isolate. see page 10
5) Solder the brown lead of the mains transformer to the mains switch. see fig. 3 page 11
6) Solder the blue lead of the mains transformer to the mains switch. see fig. 3 page 11
WIRING UP THE SPEAKER OUTPUTS
1) Before you start, you must first select the correct output transformer setting to match your loud
speakers, be it 4 ohms or 8 ohms. Most speaker use the 8 ohms setting.
2) Connect up the black BFA speaker post to the following.
a) PCB tab 5, using 1/1.13 black wire. see page 8
b) Blue leadout of the output transformer. see page 10
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c) Chassis earth solder tag, located on fixing bolt of mains transformer, using 1/1.13 black wire.
see page 10
3) Connect up the red BFA speaker post to the following.
a) For 4 ohm setting, connect the purple leadout from the O/P T. OR for 8 ohm setting, connect the
red leadout from the O/P T. N.B. NEVER connect the 4 ohm & 8 ohm leads together or you will
damage the O/P T. Always isolate the lead you are not using. see page 10.
b) Cut a length of single screened cable at 60cm, expose 2cm of one end, remove the screened
portion as this is not needed, and wire up the red signal wire to the speaker`s red terminal.
Exposed 2cm of the other end, wire up the red signal wire to PCB tab 8 and the screened
portion to PCB tab 7. see page 8
WIRING THE PCB TO EXTERNAL CONNECTIONS
1) Refer to page 8 closely and solder all remaining 13 external joins to the PCB.
2) With all mains transformer connections, tab 4, 13 to 19 it is a good idea to twist up the relevant
winding leads to reduce the likelyhood of hum. Thus, twist together the following: white and
orange, twist red, red and black and lastly twist yellow, yellow and grey(thick). see page 10
TABLE SHOWS PCB TO EXTERNAL CONNECTIONS
tab no. label on PCB external connection to:
1 brown wire from mains lead
2 brown wire to mains switch
3 earth wire from mains lead
4 mains transformer secondary grey wire(thick) earth connection
5 black BFA speaker post
6 A black wire from output transformer
7 GND ground of feedback screened wire
8 FB signal of feedback screened wire
9 GND ground of signal screened wire
10 I/P signal of signal screened wire
11 A white wire from output transformer
12 CT 2 x orange wire from output transformer
13 black wire from mains transformer
14 1 x red wire from mains transformer
15 1 x red wire from mains transformer
16 1 x yellow wire from mains transformer
17 1 x yellow wire from mains transformer
18 white wire from mains transformer
19 orange wire from mains transformer
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FIRE UP TIME
1) Now you are ready to fire her up. A useful piece of equipment to use at this stage is a Variac
(rated at 2 Amps or over), to limit the initial voltage input. If you cannot get one do not worry
most budding kit builders are armed with only a multimeter, this is sufficient. It is a good idea to
have a dummy load, a 4 or 8 ohm high wattage resistor depending on how you have set it up, or
an old pair of speakers connected up to the BFA speaker terminals.
2) The next step is to PUT ON THE SAFETY GLOVES PROVIDED TO PREVENT ANY RISK OF
RECEIVING ANY ELECTRIC SHOCKS.
3) Switch her on and step back, do not be put off by a slight tinkering sounds this is the noise of
the valves warming up. You should see two small red points of light in each valve, these are the
valve heaters.
4) When the amplifier is working, measure all voltages to ensure they are correct, measure with 0
volts signal input, bearing in mind that a degree of variation (around 15%) is to be expected due
to dependence upon the mains voltage. KEEP YOUR GLOVES ON.
5) Once fully tested fix the two chassis parts together, using the M3 x 10 flat head screws
provided, then fix in place the self adhesive feet.
6) Now you can enjoy the wonders of the KEL 80.
TABLE SHOWS TEST VOLTAGES
voltage
reading label on PCB position on PCB
1.5Vdc k V6 pin 7
125Vdc a V6 pin 5
225Vdc a1 V5 pin 1
225Vdc a2 V5 pin 9
130Vdc k1, k2 V5 pin 3, 6
9Vdc g3, k V1 pin 1, 8
9Vdc g3, k V2 pin 1, 8
9Vdc g3, k V3 pin 1, 8
9Vdc g3, k V4 pin 1, 8
-10Vdc g1 V1 pin 5, V2 pin 5, V3 pin 5, V4 pin 5
255Vdc g2 V1 pin 4, V2 pin 4, V3 pin 4, V4 pin 4
505Vdc a V1 pin 3, V2 pin 3, V3 pin 3, V4 pin 3
6.3Vdc h to h 6AU6 heater voltage: V6 pin 3 to pin 4
6.3Vac h to h 5687 heater voltage: V5 pin 4 to pin 8 or pin 5 to pin 8
6.3Vac h to h EL34 heater voltage: V1, V2, V3, V4 pin 2 to pin 7
FAULTS AND HOW TO CLEAR THEM
1) Any serious faults will blow the mains fuse immediately. That is your guarantee. Do not
squander it by fitting a larger fuse in frustration, because the situation will get worse not better.
2) The most common mistake will be one of the following:
a) a wrongly placed component
b) a solder link forgotten
c) a component not soldered in place
d) an external to PCB connection wrongly placed
3) To start with turn the power switch off and pull the mains plug out. A way to remedy these
possible faults is to go through the instructions and visually check everything. Always wear your
gloves even though the power is off as some residual charge may be held within the power
supply capacitors. You may need to take out the PCB to access the valve base side.
4) If you are still having problems then call the helpline.
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PARTS LIST(for 2 off)
component description quantity bag No. location in amp
R1 3.9K, 6W 2 1 PCB
R2 33K, 3W 2 2 PCB
R3 13K, 0.5 2 3 PCB
R4 36K, 0.5W 2 4 PCB
R5 100R, 1W 2 5 PCB
R6 100R, 1W 2 5 PCB
R7 180R, 7W 2 6 PCB
R8 180R, 7W 2 6 PCB
R9 3.3K, 0.5W 2 7 PCB
R10 3.3K, 0.5W 2 7 PCB
R11 100R, 1W 2 5 PCB
R12 not used N/A N/A N/A
R13 180R, 7W 2 6 PCB
R14 180R, 7W 2 6 PCB
R15 3.3K, 0.5W 2 7 PCB
R16 3.3K, 0.5W 2 7 PCB
R17 220K, 0.5W 2 8 PCB
R18 220K, 0.5W 2 8 PCB
R19 10K, 3W 2 9 PCB
R20a 68K, 1W 2 10 PCB
R20b 82K, 1W 2 11 PCB
R21 15K, 1W 2 12 PCB
R22 15K, 1W 2 12 PCB
R23 1M, 0.5W 2 13 PCB
R24 390R, 0.5W 2 14 PCB
R25 330R, 0.5W 2 15 PCB
R26 27R, 0.5W 2 16 PCB
R27 39K, 3W 2 17 PCB
R28 100R, 0.5W 2 18 PCB
R29 2.2K, 0.5W 2 19 PCB
R30 1K, 0.5W 2 20 PCB
R31 100K, 0.5W 2 21 PCB
R32 100R 1W 2 5 PCB
C1 470uF 450V 2 22 PCB
C2 470uF 450V 2 22 PCB
C3 4700uF 16V 2 23 PCB
C4 100uF 35V 2 24 PCB
C5 100uF 450V 2 25 PCB
C6 100uF 450V 2 25 PCB
C7 220uF 25V 2 26 PCB
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KEL80 instructions 27/3/00 10:44 am Page 8

PARTS LIST
component description quantity bag No. location in amp
C8 220uF 25V 2 26 PCB
C9 220uF 25V 2 26 PCB
C10 220uF 25V 2 26 PCB
C11 0.68uF 630V 2 27 PCB
C12 0.68uF 630V 2 27 PCB
C13 1uF 250V 2 28 PCB
C14 470uF 10V 2 29 PCB
C15 470pF 160V 2 30 PCB
BR1 2 31 PCB(device SKB B500 C3200/2200)
BR2 2 31 PCB(device 2KBP02M)
BR3 2 31 PCB(device WO2G)
HARDWARE
mains switch 2 32 FRONT PANEL
fuse holder 2 32 PCB
fuse holder cover 2 32 PCB
fuse, 1.6A 2 32 PCB
M3 x 10 screws 24 32 to fit PCB and base plate to chassis
M3 fibre washers 12 32 to fit PCB
self adhesive clips 10 32 securing of wires
mains trans. fittings 2 32 to fit mains transformer to chassis
red phonos 1 32 BACK PANEL
black phonos 1 32 BACK PANEL
M6 fibre washer. 4 33 BACK PANEL for isolating phono
sockets
strain relief 2 33 for fixing of the mains lead to the
chassis
BFA speaker term. 2 33 BACK PANEL
M5 solder tag 2 33 chassis earth connected to
output transformer bolt
PCB terminal pins 30 33 PCB
B9A valve base 2 33 PCB
B7G valve base 2 33 PCB
octal valve base 8 34 PCB
Wire
1/0.6 black wire 350cm 35 wiring of 6AU6 & 5687 heaters &
all pin pts. & link
1/1.13 black wire 300cm 35 wiring of EL34 heater & earth of
spk. term , chassis
single screened wire 120cm 35 wiring of phono inputs & feedback links
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KEL80 instructions 27/3/00 10:44 am Page 9

component description quantity bag No. location in amp
6AU6 2 on V6 valve base (on PCB)
5687 2 on V5 valve base (on PCB)
EL34 8 on V1, V2, V3, V4 valve bases (on PCB)
mains transformer 2
output transformer 2
PCB 2
safety gloves 1 pair
maind lead 2
chassis(2 parts) 2
instruction manual 1
ALTERATIONS TO KEL80 INSTRUCTIONS
Wiring up tab 2 to mains switch:
a) Insert the terminal pin to tab 2 so that it projects into the valve base side of the PCB and solder
both side.
b) Solder one end of the 25cm brown wire (excess from the mains lead) to tab 2.
c) Solder the other end of the brown wire to the mains switch later once the PCB is ready for fitting.
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